1. Field of the Invention
The present invention relates to a double action/cylinder unit in which the piston is guided in the cylinder and is attached to a piston rod. The cylinder is to be charged with a pressure agent, particularly hydraulic fluid via a first fitting at a first end face, the pressure agent being fed through the first fitting in a controlled manner and the cylinder is to be charged at another, second end face with a pressure agent via a second fitting which is in communication with an annular chamber formed by the central section of the piston rod, the inner wall of the cylinder, a second end face of the piston and a cylinder end piece, the second fitting providing communication between the annular chamber and a pressure agent reservoir.
2. Description of the Prior Art
Such piston/cylinder units of the type set forth above are generally hydraulically operated and, in accordance with standard terminology employed in practice shall be referred to below as a hydro-cylinder.
Double action hydro-cylinders heretofore always had two fittings for the pressure agent respectively located at the end sections of the cylinder, i.e. fittings usually for hydraulic fluid, between which a connecting line with a corresponding reverse valve was provided and with which each of the first or second piston end face was to be selectively charged dependent on the desired position of the piston rod. The control valve, the connecting line and the second fitting, etc., are, however, a matter of component parts which are definitely of considerable expense for such hydro-cylinders and which lead to a great cost reduction when they can be eliminated. In addition, a second pressure agent fitting for a second pressure agent line was also not desired for reasons of assembly, space and the like, particularly given apparatus to be equipped with such double action hydro-cylinders which must otherwise be designed in an extremely cost-effective manner in order to be competitive in the marketplace.
Consequently, a piston/cylinder unit without a second fitting and, of course, without a corresponding connecting line and without a correspondingly-complicated control valve, etc., has been developed and the return of the piston rod is effected by way of an externally-disposed spring. Given the embodiment discussed herein, this spring is placed under tension when the piston is charged with the pressure agent. When the charging of the pressure agent is discontinued and the connecting line for reflow is released, then, given such a hydro-cylinder, the spring under corresponding tension in this extended position sees to it that the piston rod returns to its initial position.
Such externally-disposed tension springs, however, are extremely undesirable in numerous applications. They are not only considered dangerous by the trade associations (and therefore need a certain encapsulation or the like, this increasing the expense) but are also not welcomed by the users, apart from the fact that such a design makes a rather provisional impression and is also exposed to a variety of disruptive influences.
For the above reasons, hydro-cylinders having so-called hydraulic accumulators have been developed, i.e. the second fitting has in fact been provided, as in the embodiment initially described, but is not connected to a connecting line for a pressure agent, but rather to a hydraulic accumulator. The hydraulic accumulator will be explained in greater detail below with reference to the illustrative embodiment of the present invention, the accumulator comprising an essentially closed housing in which a diaphragm is disposed, a pressurized gas (generally nitrogen) being located on one side of the diaphragm in a closed chamber defined by the corresponding housing section and the diaphragm, whereas the opposite side of the diaphragm is connected to the remaining part of the housing comprising the fitting, this connection being effective by way of that fitting of the cylinder. When the hydraulic accumulator is charged with a pressure agent of the hydro-cylinder via its fitting, then the pressure agent compresses the gas in its chamber upon deformation of the diaphragm and builds up a corresponding pressure which, dependent on the pressure conditions prevailing at the fitting of the hydraulic accumulator, can definitely be discharged, in turn, to the exterior, i.e. into the annular chamber of the hydro-cylinder in this case.
Such hydro-cylinders of the type having a hydraulic accumulator have been well received, particularly since the hydraulic accumulators are currently manufactured in such high piece numbers that the unit price is relatively low. However, they still have the substantial disadvantages which particularly reside in the fact that, when the operations are initiated, a filling of the annular chamber and of the hydraulic accumulator with a pressure agent must be carried out first and, over and above all else, that due to the constantly persisting leakage losses (of hydraulic fluid) at the piston rod and, or at the piston side, a pressure decrease arises in the system of the annular chamber/hydraulic accumulator which necessarily leads to an outage of the piston/cylinder unit after a certain operating time.